When homogenization is complete, the milk is cooled to between 43-46° C and the starter cultures are added in a concentration of about 2%. It is held at this temperature for about three to four hours , while the incubation process takes place. During this time, the bacteria metabolizes certain compounds in the milk producing the characteristic yogurt flavor. An important byproduct of this process is lactic acid.the incubation process is done either in a large tank of several hundred gallons and The yogurt is cooled to 7°C to stop the fermentation process.